1. Field of the Invention
The present invention relates to a method of manufacturing fatty acid esters of polyoxyalkylene alkyl ethers and, more particularly, to a method of manufacturing fatty acid esters of polyoxyalkylene alkyl ethers obtained such that a fatty acid alkyl ester and an alkylene oxide are directly reacted with each other using a magnesium oxide catalyst added with a metal ion.
2. Description of the Related Art
Fatty acid esters of polyoxyalkylene alkyl ethers are known an ether ester-type nonionic surfactant. Of all fatty acid esters of polyoxyalkylene alkyl ethers, polyoxyethylene stearyl ether stearates having the following formula, for example, is used as an emulsion, a dispersant, or an oil-phase adjustor in cosmetics or in a variety of industrial fields: ##STR2##
Use of polyoxyethylene methyl ether laurates originated from a lower alkyl ether having the following formula as a wetting agent has been studied (JAOACS, 56:873 (1973)): ##STR3##
A polyoxyethylene alkyl ether and a polyoxyethylene fatty acid ester as typical ethylene oxide type nonionic surfactants can be obtained such that an alcohol and a fatty acid are respectively used as starting materials, and ethylene oxides are directly addition-polymerized in the presence of an alkaline or acidic catalyst.
To the contrary, in fatty acid esters of polyoxyalkylene alkyl ethers, even if it is attempted to react an alkylene oxide with a fatty acid alkyl ester (RCOOR') in the presence of an alkaline or acidic catalyst, addition polymerization of the alkylene oxide does not progress. For this reason, after an alcohol is reacted with an alkylene oxide to prepare a polyoxyalkylene alkyl ether, this polyoxyalkylene alkyl ether is reacted with a fatty acid or fatty acid alkyl ester, thereby performing esterification. That is, a two-step reaction is employed.
Alternatively, fatty acid is reacted with alkylene oxide to produce polyoxyalkylene fatty acid ester, and the end of thus produced ester is alkylated to produce fatty acid ester of polyoxyalkylene alkyl ether. In this method, however, much by-products are produced and the content of monoester is about 50%.
The following examples of a one-step reaction between a fatty acid alkyl ester and an alkylene oxide for manufacturing fatty acid esters of polyoxyalkylene alkyl ethers have been reported.
(1) Alkyl acetate is reacted with an alkylene oxide by using a calcinated hydrotalcite compound as a catalyst to synthesize acetic acid ester of polyoxyalkylene alkyl ether (Published Unexamined Japanese Patent Application No. 56-36431).
(2) Using a catalyst consisting of a metal halide of, e.g., zinc or aluminum or consisting of an organometallic compound containing zinc or aluminum, or a combination of such a catalyst and an amine compound, an alkylene oxide is reacted with a carboxylate to manufacture a fatty acid ester of polyoxyalkylene alkyl ether (Published Examined Japanese Patent Application No. 53-24930). For example, using a catalyst consisting of triethyl aluminum or a combination of aluminum chloride and triethyl amine, ethyl acetate is reacted with an ethylene oxide to prepare acetic acid ester of polyoxyethylene ethyl ether.
(3) Ethyl acetate is reacted with an excessive amount of ethylene glycol monoethyl ether in the presence of a strong-acidic cation exchange resin to manufacture acetic acid ester of polyoxyethylene ethyl ether (Published Unexamined Japanese Patent Application No. 54-1038125).
In these methods, however, colored products are obtained and it is difficult to separate the catalyst from the reaction products, thus resulting in unsatisfactory industrial applications.